There is known a technology for illuminating the lower side of a side surface of a door of a vehicle by means of a lamp incorporated in a door mirror (see Patent Literatures 1 to 4). The lamp employs a luminous filament, and the normal life span of the filament itself is approximately several hundreds to 1000 hours. A lamp reaching the end of its life causes a lighting failure generated by filament breakage. It is assumed that the lamp reaches the end of its life during a long duration of use of the lamp in a vehicle, in which case the lamp needs to be replaced. Particularly, the life of the lamp tends to be shortened by vibration or shock of a moving vehicle, which increases the need for lamp replacement.    Patent Literature 1: Japanese Patent Application Publication No. 2001-294081.    Patent Literature 2: Japanese Patent Application Publication No. 2002-96683.    Patent Literature 3: U.S. Pat. No. 6,074,077.    Patent Literature 4: U.S. Pat. No. 6,299,333.